Much prior art has addressed the development of thickened household laundry products such as detergents and bleaches. Consumer preference for such thickened products is well documented, and applications include prewash products and hard surface cleaners which require concentrating the active ingredients and/or the capability to cling to surfaces. Typical thickeners of the prior art include surfactants, polymers, or combinations thereof. A number of disadvantages are associated with such prior art thickening systems. For instance, to the extent that a thickened laundry product requires the addition of components solely for thickening, the cost of the product is increased. Moreover, many prior art thickeners are incompatible with non-chloride bleaches, such as peroxygen or peracid bleaches.
Generally, prior art thickened compositions incorporating fluorescent whitening agents require a high solids (fluorescent whitening agent) content, or additional components, such as polymers, to achieve sufficient thickening. In addition, aqueous suspensions of fluorescent whitening agents of the art are usually not stable at acidic pHs.
A thickening system which overcame some of these deficiencies by incorporating low levels of a fluorescent whitening agent as part of the thickening system was described in U.S. Pat. No. 4,764,302, inventors Baker et al. One embodiment of the Baker et al. aqueous bleach composition system comprises a nonionic polyethoxylated alcohol surfactant, an acid insoluble fluorescent whitening agent, and a soap to synergistically increase viscosity. Preferred surfactants include polyethoxylated alcohols manufactured by the Shell Chemical Company under the tradename "Neodol." Neodol 25-7, which is a mixture of 12 to 15 carbon chain length alcohols with about 7 ethylene oxide groups per molecule, is particularly suitable.
The Baker thickener can be used to thicken a variety of liquid laundry product compositions that contain bleaches and detergents. Typically, the thickening system is used in amounts effective to attain an intermediate viscosity (200-500 centipoise) for products such as hard surface cleaners which need sufficient residence time for use on non-horizontal surfaces. More typically, the thickening system may be formulated to have a viscosity on the order of 100-300 centipoise for use with a laundry product to enhance pourability and allow concentration of the product on heavily stained fabrics. The bleach used preferably is a peroxygen or peracid bleach, although virtually any oxidant capable of operating at acidic pHs could be used.
Despite these advantages, thickened liquid laundry products often exhibit freeze-thaw instability which is characterized by marbling and flaking of the final consumer product.